Lithium ion battery utilizing carbon foam electrodes

ABSTRACT

A lithium ion battery ( 200 ) has at least two carbon foam electrodes ( 54, 56 ). Each of the electrodes ( 54, 56 ) is fitted with a plate ( 60, 62  respectively) formed from an electrically conductive material. The plate ( 60, 62 ) has an underside which is formed so as to be attached to one end of the carbon foam electrode ( 54, 56 ). The plate ( 60, 62 ) may be fixed to the electrode by crimping or a similar deforming process or may be fitted thereto by an electrically conductive adhesive.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention is directed to high energy lithium ion batteries.More particularly, the present invention is directed to such a highenergy density battery which incorporates carbon foam electrodes witheach electrode having attached thereto an electrical contact plate.

2. Discussion

The dual graphite lithium battery was originally developed in the early1980's in an effort to provide a lightweight energy source capable ofdelivering very high energy density. The driving force behind thedevelopment of the lithium ion battery has been for some time the needfor a lightweight and rechargeable power source embodying a high energydensity for use in small electronic devices such as laptop computers andvideo cameras.

Additional applications of batteries demonstrating high energy densityand light weight are being considered and explored. Specifically,electric vehicle applications are thought to be a promising use of thistype of power source.

Electric vehicles, of course, are not new. Electric cars were introducedin the early 20th century which utilized aqueous-electrolyte type leadbatteries. Lead batteries were satisfactory then (and remainsatisfactory today) with respect to their good rechargeability. Becauseof the poor weight-to-energy-density ratio of the lead battery, theseearly electric vehicles proved slow and incapable of long distanceoperation.

Electric vehicles have traditionally been anachronistic, and, whileoffering the same modern appearance as their counterparts, havecontinued to suffer from the lead battery's excessive weight and lowenergy density.

These problems have forced a shift in research to the lithium battery.Given the demand for a rechargeable secondary battery having anattractive energy density-to-weight ratio, much energy has been expendedin studying various types of cells. Rechargeable lithium cells of manyvarieties have generated much interest. But the results have not beenentirely promising. For example, rechargeable, nonaqueous electrolytecells using lithium metal negative electrodes have presented severalproblems. Such batteries demonstrate poor fast charging properties andare notorious for their short cycle life. Great concern also exists forthe inherent safety of the lithium battery largely the result of theirregular plating of lithium metal as the battery is cycled.

To overcome these problems while providing a power source that hasapplication in electric vehicle technology, rechargeable batteries basedon lithium intercalation are being researched. The lithium ion-basedsecondary cell is a nonaqueous secondary cell. Typically, lithium or alithium salt is provided as an ion source which is intercalated into acarbon electrode to create a positively charged electrode.

Lithium ion batteries provide several advantages over known leadbatteries, such as small self-discharge characteristics and, at leastwhen compared to lead batteries, environmental safety. But the greatestadvantage of lithium ion batteries over the known lead battery forvehicle application is attractive energy-density-to-weight ratio. Beinglightweight while offering high energy density, the lithium ion batteryis thought to have great potential in electric vehicle applications.

The cathode in a conventional lithium ion battery (typically a metaloxide such as Mn₂O₄, CoO₂, or NiO) is doped with lithium. Theconventional lithium ion battery uses a lithium salt (typically LiPF₆ orLiClO₄) dissolved in one or more organic solvents. When dissolved, thesalt in the electrolyte is split into the positive ion and negativecation (depending on the salt used). The lithium ambient graphite fiberbattery positive ion is intercalated into the carbon anode and thenegative ion is intercalated into the carbon cathode.

When a charge is applied to the positive and negative electrodes, thelithium from the cathode is transported from the cathode as an ion andis intercalated into the anode (carbon or lithium metal). Voltage iscreated by the difference in potential of the positively charged anodeand the negatively charged cathode.

On discharge, the process is reversed and lithium ions flow from theanode into the liquid electrolyte as do the negative ions from thecathode. The cell is balanced by equal parts of positive and negativeions absorbed back into the electrolyte.

Since the lithium ion moves from one electrode to the other to storeenergy the lithium ion battery is commonly known as a “rocking chairbattery.” The lithium ambient graphite fiber battery uses the sameprincipal of intercalation for the positive electrode (carbon) and usesit again for the negative electrode (carbon). This is in lieu of alithium doped metal oxide.

The lithium ambient graphite fiber battery is thought to be moreattractive in electric vehicle applications. The lithium ambientgraphite fiber battery, for example, is safer in principal than thelithium ion battery. In addition, while demonstrating a comparabletheoretical energy density to the lithium ion battery, the lithiumambient graphite fiber battery will demonstrate more recharge cyclesthan a lithium ion battery.

A number of patents have issued which teach the general construction ofthe lithium ion battery. Such patents include, for example: U.S. Pat.No. 5,631,106, issued on May 20, 1997, to Dahn et al. for ELECTRODES FORLITHIUM ION BATTERIES USING POLYSILAZANES CERAMIC WITH LITHIUM; U.S.Pat. No. 5,721,067, issued on Feb. 24, 1998 to Dasgupta et al. forRECHARGEABLE LITHIUM BATTERY HAVING IMPROVED REVERSIBLE CAPACITY; U.S.Pat. No. 5,705,292, issued on Jan. 6, 1998 to Fujiwara et al. forLITHIUM ION SECONDARY BATTERY; U.S. Pat. No. 5,677,083, issued on Oct.14, 1997, to Tomiyama for NON-AQUEOUS LITHIUM ION SECONDARY BATTERYCOMPRISING AT LEAST TWO LAYERS OF LITHIUM-CONTAINING TRANSITIONAL METALOXIDE; U.S. Pat. No. 5,670,277, issued on Sep. 23, 1997, to Barker etal. for LITHIUM COPPER OXIDE CATHODE FOR LITHIUM CELLS AND BATTERIES;U.S. Pat. No. 5,612,155, issued on Mar. 18, 1997, to Asami et al. forLITHIUM ION SECONDARY BATTERY; U.S. Pat. No. 5,595,839, issued on Jan.21, 1997, to Hossain for BIPOLAR LITHIUM-ION RECHARGEABLE BATTERY; U.S.Pat. No. 5,587,253, issued on Dec. 24, 1996, to Gozdz et al. for LOWRESISTANCE RECHARGEABLE LITHIUM-ION BATTERY; U.S. Pat. No. 5,571,634,issued on Nov. 5, 1996, to Gozdz et al. for HYBRID LITHIUM-ION BATTERYPOLYMER MATRIX COMPOSITIONS; U.S. Pat. No. 5,567,548, issued on Oct. 22,1996, to Margalit for LITHIUM ION BATTERY WITH LITHIUM VANADIUMPENTOXIDE POSITIVE ELECTRODE; U.S. Pat. No. 5,554,459, issued on Sep.10, 1996, to Gozdz et al. for MATERIAL AND METHOD FOR LOW INTERNALRESISTANCE LITHIUM ION BATTERY; U.S. Pat. No. 5,547,782, issued Aug. 20,1996, to Dasgupta et al. for CURRENT COLLOZION FOR LITHIUM ION BATTERY;U.S. Pat. No. 5,496,663, issued on Mar. 5, 1996, to Margalit et al. forLITHIUM VANADIUM PENTOXIDE POSITIVE ELECTRODE; and U.S. Pat. No.5,478,668, issued on Dec. 26, 1995, to Gozdz et al. for RECHARGEABLELITHIUM BATTERY CONSTRUCTION.

Also among this group are several patents to McCullough, McCullough etal., or McCullough, Jr. et al. which include: U.S. Pat. No. 4,631,118,issued on Dec. 23, 1986, for LOW RESISTANCE COLLECTOR FRAME FORELECTRODONDUCTIVE ORGANIC, CARBON AND GRAPHITIC MATERIALS; U.S. Pat. No.4,830,938, issued on May 16, 1989, for SECONDARY BATTERY; U.S. Pat. No.5,503,929, issued Apr. 2, 1996, for LINEAR CARBONACEOUS FIBER WITHIMPROVED ELONGABILITY; U.S. Pat. No. 5,532,083, issued on Jul. 2, 1996,for FLEXIBLE CARBON FIBER ELECTRODE WITH LOW MODULUS AND HIGH ELECTRICALCONDUCTIVITY, BATTGERY EMPLOYING THE CARBON FIBER ELECTRODE, AND METHODOF MANUFACTURE; and U.S. Pat. No. 5,518,836, issued May 21, 1996, forFLEXIBLE CARBON FIBER, CARBON FIBER ELECTRODE AND SECONDARY ENERGYSTORAGE DEVICES.

Particularly, the graphite component has taken on a variety of forms asevidenced by the prior art. For example, a supercapacitor based oncarbon foams has been illustrated in U.S. Pat. No. 5,260,855, issued onNov. 9, 1993, to Kaschmitter et al.x

While generally improving the state of the art, known battery designsincorporating carbon foam electrodes have not eliminated the need for apractical lithium battery construction.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a lithium ionbattery incorporating carbon foam electrodes.

A further object of the invention is to provide a practical electricalcontact on each of the carbon foam electrodes.

Another object of the invention is to provide an electrical contacthaving a channel formed therein for placement on and partially around anend of the carbon foam electrode.

Other objects and advantages will become apparent from the followingdetailed description and accompanying drawing. Basically, the inventioncomprises a battery having at least two carbon foam electrodes. Each ofthe electrodes is fitted with a plate formed from an electricallyconductive material. The plate has an underside which is formed so as tobe attached to one end of the carbon foam electrode. The plate may befixed to the electrode by crimping or a similar deforming process.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood by reference to thefollowing detailed description of the preferred embodiments of thepresent invention when read in conjunction with the accompanyingdrawings, in which like reference characters refer to like partsthroughout the view, and in which:

FIG. 1 is a schematic illustration of a battery having carbon foamelectrodes according to the present invention;

FIG. 2 is a sectional view of a dual carbon foam electrode batteryaccording to its preferred embodiment;

FIG. 3 is a perspective view of a pair of carbon electrodes separated byan electrode separator and spaced apart therefrom; and

FIG. 4 is a perspective view of a single electrode according to analternate embodiment of the present invention illustrating the contactplate in spaced apart relation with respect to the carbon foamelectrode;

FIG. 5 is a perspective view of the single electrode of FIG. 4illustrated as an assembly;

FIG. 6 is a cross-section of a dual carbon foam electrode batteryaccording to the present invention;

FIG. 7 is a schematic of an alternate arrangement of electrodes within abattery case; and

FIG. 8 is a perspective view of a battery incorporating a plurality ofelectrodes according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawings disclose the preferred embodiment of the present invention.While the configurations according to the illustrated embodiment arepreferred, it is envisioned that alternate configurations of the presentinvention may be adopted without deviating from the invention asportrayed. The preferred embodiment is discussed hereafter.

FIG. 1 illustrates a schematic of an exemplary battery having carbonfoam electrodes, the battery being generally illustrated as 10, formedaccording to the present invention. The battery 10 includes a pair ofspaced carbon foam electrodes 12, 14, separated by an electrodeseparator 16. A pair of spaced electrical contacts 18, 20 provide anelectrical connection with an electrically driven component 24. Theseparator 16 may be made of a polymerized material such aspolypropylene, Teflon (registered trademark), or nylon.

A variety of carbon foam materials may be used in the present invention.The preferred foams have porosities of between 10 and 100 ppi, althoughother porosities might be used. An exemplary but not limiting foam isproduced by Oak Ridge Natinoal Laboratory's Metals and CeramicsDivision. Such typical properties include a micrographic porosity (ppi)of 58.8, an ash content of 0.39 (weight percent at 1000 degreescentigrade), a bulk density of 0.042 (g/cm³), a ligament density of1.538 (g/cm³), a surface area of 1.623 (m2/g), a resistivity of 0.75(ohm-cm), and a specific heat of 0.30 (cal/g/degrees centigrade). Themaximum usable temperature in air is 350 degrees centigrade, while themaximum usable temperature in an inert environment is 3500 degreescentigrade. Such materials demonstrate a thermal expansion of 1.15(ppm/degree centigrade) at 0-200 degrees centigrade, 1.65 (ppm/degreecentigrade) at 0-500 degrees centigrade, and 1.65 (ppm/degreecentigrade) at 0-1000 degrees centigrade. Importantly, these samplesdemonstrated the following thermal conductivities: 0.085 (W/m-K) at 200degrees centigrade, 0.125 (W/m-K) at 300 degrees centigrade, 0.180(W/m-K) at 400 degrees centigrade, 0.252 (W/m-K) at 500 degreescentigrade, 0.407 (W/m-K) at 650 degrees centigrade, and 0.625 (W/m-K)at 800 degrees centigrade.

The selected carbon foams are very strong and retain their shapes. Forexample, the tested foams demonstrated compressive strengths (at 20degrees centigrade) of 625 kPa with a 10 percent deflection and 763 kPawith ultimate deflection. The tested foams also demonstrated shearstrength (at 20 degrees centigrade) of 290 kPa and tensile strength(also at 20 degrees centigrade) of 810 kPa. Flexure strength (at 20degrees centigrade) was demonstrated as being 862 kPa while a flexuremodulus of 58.6 (MPa) was shown. Of course, other foams including othersilicon carbide foams might be used having different characteristicswhile still falling within the spirit and scope of the presentinvention.

FIG. 2 is a sectional view of a dual carbon foam electrode battery,generally illustrated as 50, constructed according to its preferredembodiment of the present invention. The battery 50 includes a case orhousing 52 made of a known structurally rigid material such as rubber orplastic. A pair of spaced carbon foam electrodes 54, 56 is positionedwithin the hollow defined by the body 52. The electrodes 54, 56 arecomposed of open-cell carbon foam having selected porosity. The porosityis selected so as to provide a specific amount of surface area. Thespectrum of pore size is relatively broad and includes a possible rangeof from between 10 and 500 pores per inch (ppi).

An electrode separator 58 is positioned between the electrodes 54, 56.The separator electrically insulates the electrodes 54, 56 from thenonionic conduction of electricity.

At one end of each of the electrodes 54, 56 is fitted with electricalcontacts 60, 62, respectively. The contacts 60, 62 provide electricalenergy to an external component to be driven by the battery 50.Preferably the contacts 60, 62 are composed of a highly conductivematerial such as copper, although other conductive metals such as brassor aluminum may be used as well.

Liquid electrolytes conventionally used in Li-ion batteries containorganic solvents and conducting salts. The organic solvents aregenerally carbonates. Probably the most commonly used conducting salt islithium hexafluorophosphate (LiPF₆), although other commonly-used saltsinclude LiBF₄, LiAsF₆ and LiClO₄.

FIG. 3 is a perspective view of the pair of carbon electrodes 54, 56separated by the electrode separator 58. The electrode contact plate 60includes a top wall 64 and a pair of opposing, spaced apart side walls66, 68. A channel 70 is defined by the top wall 64 and the pair ofspaced apart side walls 66, 68. The channel 70 is mated with one end 72of the carbon foam electrode 54. Preferably, a pair of opposed sidechannels 74, 76 (seen more clearly in FIG. 4, discussed below) aredefined along the upper end sides of the electrode 54 for mating withthe channel 70. An extended rigid contact point 78 is provided forexternal application of electrical power. While FIG. 3 (and FIG. 4,discussed below) illustrate the contact point 78 as being positionedgenerally in the middle of the upper side of the electrode contactplates 60, 62, the contact point 78 may be positioned at, for example,the approximate ends of the plates 60, 62. As an alternative or as asupplement, a flexible contact lead 80 composed of a material such as acopper mesh may be fitted for external engagement.

According to the embodiment of FIG. 3, the sidewalls 66, 68 of thecontact plate 60 may be pinched inwardly toward one another upon thefoam electrode 54 (or 56) to mechanically grip the electrode's upperend.

FIG. 4 is a perspective view of an alternate embodiment of an electrodeassembly, generally illustrated as 100, according to the presentinvention. The electrode 100 includes a contact plate 102 in spacedapart relation with respect to a carbon foam electrode 104. (Althoughonly one electrode 100 and one contact plate 102 is illustrated, theother electrode [not shown] and the other contact plate [also not shown]is substantially the same.)

An adhesion layer 106 may be provided between the carbon foam electrode104 and the contact plate 102. The layer 106 is used in lieu of (or as asupplement to) the mechanical method of attaching the plate to theelectrode discussed above with respect to FIG. 3. The adhesion layer 106is to be composed of an electrically conductive material whichdemonstrates adhesive properties. Such materials might be nickel,silver, copper, aluminum or any electrocoated material demonstratingboth adhesive and conductive properties.

As a possible addition, a polymeric insulating layer 108 may be providedto seal the contact plate 102. The insulating layer 108 should becomposed of a polycarbonate or may be composed of any organic materialsuitable for the purpose.

FIG. 5 is a perspective view of the electrode assembly 100. Asillustrated, the insulating layer 108 essentially forms an insulatingcap over the top end of the assembly 100.

FIG. 6 is a cross-section of a dual carbon foam electrode battery,generally illustrated as 200, according to the present invention. Thebattery 200 includes a battery case 202 which includes two cells 204,206. Two electrode assemblies of the type shown in FIGS. 4 and 5 anddiscussed with respect thereto, shown here as 100, 100′, are positionedone each in the cells 204, 206. An electrolyte solution is providedwithin the battery 200 approximately up to the illustrated level 210.Preferably the level of the electrolyte is below the lower end of theinsulative layer 108. A cap 208 is preferably provided to seal the upperends of the electrodes 100, 100′ which extend outside of the batterycase 202.

It should be understood that while two electrode-filled cells areillustrated, an array of many cells such as six, ten, or twenty-four maybe substituted therefor. Such an array is illustrated in FIG. 7 which isa schematic representation of a battery according to the presentinvention. As illustrated, six cells 300, 302, 304 306, 308, 310 areillustrated. The cells 300, 304, 308 are conductively connected to acommon positive pole 312 by a common line 314, while the cells 302, 306,310 are conductively connected to a common negative pole 316 by a commonline 318.

FIG. 8 is a perspective view of the battery 200 housing the plural arrayelectrodes of FIG. 7. Of course, alternate configurations of the batterydesign, such as shape and size, may be provided.

Those skill in the art can now appreciate from the foregoing descriptionthat the broad teachings of the present invention can be implemented ina variety of forms. Therefore, while this invention has been describedin connection with particular examples thereof, the true scope of theinvention should not be so limited since other modifications will becomeapparent to the skilled practitioner upon a study of the drawings,specification and following claims.

What is claimed is:
 1. A lithium battery comprising: a battery case; atleast one carbon foam electrode having a top end, a first side and asecond side; an electrically conductive plate fitted to said top end ofsaid at least one carbon foam electrode, said plate having a top and afirst side and a second side extending from said top, said first sideextending at least partially along said first side of said carbon foamelectrode and said second side extending at least partially along saidsecond side of said electrode.
 2. The lithium battery of claim 1including an electrolyte solution provided in said battery case.
 3. Thelithium battery of claim 1 further including a conductive adhesivematerial fitted between said carbon foam electrode and said plate. 4.The lithium battery of claim 1 in which said plate includes a contactpole provided on its upper side.
 5. The lithium battery of claim 1further including an insulative later provided at least partially oversaid plate and at least partially over said carbon foam electrode. 6.The lithium battery of claim 5 wherein said insulative layer is composedof a polycarbonate material.
 7. The lithium battery of claim 5 whereinsaid insulative layer is composed of an organic material.
 8. The lithiumbattery of claim 1 wherein said battery includes at least four carbonfoam electrodes.
 9. The lithium battery of claim 1 wherein said carbonfoam electrode has a porosity of between 10 and 100 ppi.
 10. The lithiumbattery of claim 1 wherein said carbon foam electrode is silicon carbidefoam.